Enter the text here that is the new abstract information for your application. This section must be no longer than 30 lines of text. The long-term goal of this project is to identify and predict the activity of gene regulatory networks (GRN) of highly expressed genes when bacteria need to grow in nutrient-limited environments. To quantitively tackle this problem, we will use as a model system the flagellum GRN in E. coli. While a lot is known about the flagellum GRN, most of our information comes from population studies that mask the regulatory dynamics taking place within uncoordinated single cells. Consequently, this project will make use of well-known fluorescence microscopy techniques and more recent advances in microfluidics to monitor at high-resolution growth and the activity of the flagellum GRN in single cells under different environmental conditions. We have organized this proposal around one of the most intriguing aspect of our preliminary data that demonstrates that the flagellum GRN exhibits pulsating dynamics. We found that the expression of flagellar genes in wild-type cells is either ?off? over several generations or is ?on? for a much shorter period of time. We propose to determine the growth cost of single pulses in individual cells. This aim will help us to identify how modulating the dynamics of the flagellum GRN activity can be a strategy to optimize both cellular growth and the synthesis of large organelles under nutrient limited conditions. At the completion of this proposal our current knowledge on the flagellum synthesis under nutrient limited conditions will be significantly advanced and we hope that some of the newly identified principles could be used in quantitative biology to optimize the designs of synthetic circuits in fluctuating nutrient-poor environments.